A wash gel metering pump has been known (West German Utility Model No. DE-GM 75,01,055.8), in which a pump piston, which is mounted in a sealing piston, is provided with a gasket, and can be actuated via an actuating lever, is arranged on one side of a conical valve seat in a pump cylinder. The pump piston can be reset after each pump stroke by means of a coil spring supported on the valve seat. On the other side, an axially movable valve member, which is provided with a closed front wall and has a valve annular wall which is in radially elastic, sealing contact with the conical valve seat, is arranged in a cylindrical cavity of the same cylinder. A helical compression spring, which presses the valve member against the valve seat provided with a central axial bore, is arranged between the valve member and a plug closing the cavity. Aside from the fact that this prior-art metering pump is unsuitable for use as a spray pump, its design is technologically too complicated for a mass-produced article, because it consists of too many individual parts. In addition, the sealing and metering pistons mounted one inside the other require excessive actuating forces.
In another prior-art metering and spray pump (DE 38,28,811 A1), the valve annular wall that is in sealing contact with the cylindrical generated surface of a projection forming the valve seat of the discharge valve is part of a bellows and is elastic only radially, and thus it can also be lifted off only radially. The valve annular walls of the suction valve provided in different embodiments there can also be lifted off from the cylindrical generated surfaces forming their valve seat only in the radial direction during the suction stroke in order for the medium drawn in to be able to flow into the interior of the bellows between the corresponding generated surface and the valve annular wall surrounding it.
Such discharge and suction valves have proved to be unsatisfactory in practice for metering and spray pumps of this class especially because an excessive opening pressure is required in the case of sufficient closing force, on the one hand, and, on the other hand, because the quality of sealing may be compromised by particles that may become lodged between the valve annular wall and the generated surface surrounding it. Given the small size of the parts of such pumps--the diameter of a bellows is ca. 12 to 15 mm and its length is ca. 30 mm--the precision of manufacture is also often insufficient to guarantee the necessary quality of closing of the valves, especially for liquid media. Even small deviations in dimension in the range of one hundredths of one mm may lead to rejects.
The other embodiments of suction valves that can be found in the same document, in which tongue-like or plate-like closing members are provided to cover axial bores, also fail to meet the requirements imposed on such pumps in terms of reliability of operation.
The quality of sealing or closing, especially of the suction valve, is also decisive for the possibility of performing dry function testing, in which these valves must prove to be air-tight, on an automatic assembly machine. Moreover, containers that are equipped with such metering and spray pumps are subjected, for safety's sake, to drop tests, in which the valves also must prove to close reliably in order to pass the test.
Another decisive property which such metering and spray pumps must possess is the possibility of economical manufacture. Since they are manufactured in very large lots, it is necessary for these pumps to consist of the smallest possible number of individual parts with relatively wide dimensional tolerances, and these parts should be able to be assembled in the simplest manner possible.